摘要
基于矿物组分分析及静态岩石力学实验测试方法，对塔里木盆地西南部地区古近系膏泥岩取样，并进行了不同围压条件下的岩石力学实验分析。结果表明：从单轴测试条件过渡到三轴测试条件，膏泥岩样品的破裂特征从张性离散破裂逐渐转变为剪切破裂。硬石膏组分体积分数的增加能明显延缓岩石破裂的时间，提高岩石的强度极限。岩样的抗压强度与硬石膏体积分数之间具有较强正相关性，随着硬石膏体积分数从10%增加到90%，其抗压强度从120 MPa增加到了200 MPa，增幅十分明显。高地层围压条件下，膏泥岩的塑性特征比较明显，表现为具有较长的环向应变曲线段。长时间的塑性行为导致膏泥岩内部矿物发生滑移位错，类似于长期蠕变行为，从而聚集较大的额外应力，对井壁或套管造成破坏。膏泥岩地层中水平方向主应力差的差异性越大，越利于膏泥岩中矿物晶体的滑动，进而对套管造成破坏。该研究可以为厚层膏泥岩地层钻测井评价及降低钻探风险提供实验依据。
Abstract
In this paper, the rock mechanics properties of the Paleogene gypsum rocks in the southwestern Tarim Basin were analyzed by using the mineral composition analysis and static rock mechanics test. The results indicates that from the uniaxial to the triaxial conditions, the rupture characteristics of the gypsum rock samples change from brittle rupture to shear rupture. An increase in the anhydrite content can delay the weakening time of the gypsum rocks and also greatly improve the rock strength upper limit. There is a very good positive correlation between the compressive strength and anhydrite mineral component. As the anhydrite mineral component increases from 10% to 90%, its compressive strength will increase from 120 MPa to 200 MPa. The increase amount is very obvious. Under high confined pressure of formation conditions, the plasticity of the gypsum rocks is obvious, which is characterized by long cyclic strain curve. Long-term plastic behavior can lead to "slippery dislocations" within the gypsum rock′s internal minerals, similar to the long-term "creep behavior", which gathers huge "extra stresses" to cause damage to the borehole or casing. The greater the horizontal principal stress difference in the gypsum formation is, the more likely the sliding of the mineral crystals is, thus causing damage to the casing. This research can provide the experimental basis for the drilling and logging evaluation and reducing the drilling risk when drilling the thick gypsum rock formation.
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